This invention relates to a system for detecting the pitch of a voice signal, and more particularly to improvement in a system for detecting the pitch of a voice signal by real time processing.
The pitch detecting system of the present invention can be utilized for analysis and synthesization of a voice. The pitch of a voice herein mentioned is the fundamental frequency of a voiced sound, which is usually in the range of (70 to 400) Hz, and the spectrum of the voice has the properties of increasing in level at the frequency of the pitch and frequencies of its integer multiples. In a system, such as vocoder, for transmitting voice signals in coded form with high efficiency, it is necessary to accurately detect and transmit the pitch which is one of basic parameters of the voice signal; and various pitch detecting system have heretofore been proposed.
Any of the conventional systems, nevertheless, has some shortcomings such as: (1) at a portion of a nasal sound or a nasalized vowel where the pitch frequency and a first Formant are close to each other, (2) at a portion where its waveform level is not maintained steady, and (3) in a glide from a voiced sound to the next one, a component of a cycle twice or half a correct pitch cycle may often be erroneously detected as the pitch cycle, resulting in inaccuracy in the detecting of pitch.